On Thu, 23 Oct 2008 21:38:48 +0400, Sergei Shtylyov <email@example.com>
> > + unsigned int sp = (cr >> 4) & 3;
> > + unsigned int clock = gbus_clock / (4 - sp);
> > + unsigned int cycle = 1000000000 / clock;
> Hm, couldn't all these values be calculated only once?
> > + unsigned int wt, shwt;
> > +
> > + /* Minimum DIOx- active time */
> > + wt = DIV_ROUND_UP(t->act8b, cycle) - 2;
> > + /* IORDY setup time: 35ns */
> > + wt = max(wt, DIV_ROUND_UP(35, cycle));
> Same comment about calculating only once...
Yes. But are there any good place to hold calculated values? I don't
think it is not worth to allocate a local structure just for holding
such values. And this is not a critical path anyway :-)
> > + /* actual wait-cycle is max(wt & ~1, 1) */
> > + if (wt > 2 && (wt & 1))
> > + wt++;
> > + wt &= ~1;
> > + /* Address-valid to DIOR/DIOW setup */
> It's really address valid to -CSx assertion and -CSx to -DIOx assertion
> setup time, and contrarywise, -DIOx to -CSx release and -CSx release to
> address invalid hold time, so it actualy applies 4 times and so constitutes
> -DIOx recovery time. It's worth to check if the minimum cycle time is reached
> with the setup time -- for PIO mode 0, minimum setup is 70 ns, multiplying
> that by 4 gives 280 ns recovery and adding 290 ns active time gives 570 ns
> cycle while the minimum is 600 ns. Luckily, PIO0 seems the only problematic
> mode as I doubt that EBUS controller can do back-to-back IDE reads/writes
> keeping address and/or -CSx asserted in-between amounting to recovery time
> being only 2x/3x setup times -- in the worst, 2x case PIO mode 3 would also
> have too little cycle/recovery time...
Oh I had not considered the total cycle time at all... I agree with
your analysis that PIO0 is the only problematic case.
And I also noticed that the calculated shwt value can be begger than 7
(which is max SHWT value) on fast GBUS and slow drive. I will add
some check for it.
I'll address all other issues too (and send incremental patch).